The present invention relates to a printed wiring board and also a printed circuit board and an electronic apparatus which utilize the printed wiring board, and more particularly to a fluidic gas meter.
In a conventional printed wiring board for use in electronic apparatuses, as shown in FIG. 1, a conductor pattern 2 made of a conductive material is formed on a main surface of an insulating substrate 1, and a through hole 4 for an electronic part penetrates the insulating substrate 1 at a land 3. In FIG. 1, reference numeral 5 designates the printed wiring board.
As shown in FIG. 2, an electronic part 6 and an electronic device are mounted on the printed wiring board 5 at predetermined positions. Lead wires or terminals of the electronic part and others are inserted into the through holes 4 and then bonded to the lands 3 by solder to form a printed circuit board 7.
The printed circuit board 7, which is obtained by mounting the above-mentioned manner, has been used in electronic apparatuses.
In the conventional printed circuit board, however, there arise the following problems. That is, when the number of terminals of the electronic part and device mounted on the printed wiring board is increased, it is required to determine the positions of the through holes 4 accurately, and moreover it is difficult to insert the terminals of the electronic part and device into the through holes 4. Specifically, in a case where the electronic part and device are previously mounted mechanically on the frame or the like of an electronic apparatus and the terminals of the electronic part and device thus fixed are inserted into the through holes of the printed wiring board, the insertion of the terminals into the through holes is very difficult.
Next, let us consider a conventional fluidic gas meter. In the fluidic gas meter, a gas flows through a flow path structure including the so-called fluidic element which is designated by reference numeral 101 in FIG. 3, and fluidic oscillation of the gas flowing through the fluidic element is counted up to display the amount of gas consumed, because the frequency of the fluidic oscillation is proportional to the flow rate of the gas. In a case where the flow rate of the gas is extremely small, however, no fluidic oscillation is generated in the fluidic element. In this case, the flow rate of the gas is measured by a flow sensor. The amount of gas consumed due to the flow-rate measurement using the flow sensor is added to the amount of gas consumed due to the measurement using the fluidic element at an ordinary flow rate.
Referring to FIG. 3, a gas flows into the fluidic element 101 in a direction indicated by an arrow A, and the fluidic oscillation generated in the fluidic element is converted by a piezoelectric-film sensor 102 into an electric signal. In more detail, pulsating pressures at two feed-back flow paths of the fluidic element 101 are differentially applied to both surfaces of the piezoelectric film of the sensor 102, to obtain an electric signal having the same frequency as the frequency of the fluidic oscillation. A flow sensor 103 is made up of a heater to be disposed in a flow path and a pair of temperature sensors disposed on the upstream and downstream sides of the heater. The flow sensor 103 is disposed in a nozzle portion of the fluidic element 101 and determines a flow rate from the temperature difference between the temperature sensors due to the flow of a gas. The electric signal from the piezo-electric-film sensor 102 is amplified and shaped by an electronic circuit 104. On the other hand, the output signal of the flow sensor 103 is converted by an IC 105, supplementary thereto, into a pulse signal having a frequency proportional to the flow rate of the gas. A microcomputer 106 is applied with the outputs of the circuits 104 and 105, to calculate the amount of gas consumed, and a numeral indicating the amount of gas consumed is displayed by a display device 107. The fluidic gas meter does not only measure and display the amount of gas consumed, but also has a safety function of detecting abnormality in gas flow rate and gas pressure, detecting an earthquake, and cutting off a gas in case of emergency. In order to perform the safety function, the gas meter is provided with a pressure switch, a seismic sensor, a cut-off valve (that is, electromagnetic valve), an electronic circuit including a microcomputer, and a battery. Further, the electronic devices and units are connected to one another by lead wires.
In order to put the fluidic gas meter to practical use, it is necessary to mount the cut-off valve (that is, electromagnetic valve), the pressure switch, the flow sensor, the piezoelectric-film sensor, the seismic sensor and the electronic circuit on the flow path structure including the fluidic element, as one body, and to make the assembly thus obtained as small as possible. The number of lead wires from the cut-off valve, the pressure switch, the flow sensor, the piezoelectric-film sensor and the electronic circuit is very large. Accordingly, a space for the lead wires is insufficient and the lead wires are forced in a gap between devices such as the pressure switch and the cut-off valve. Thus, there arise problems that a device is damaged on the basis of the physical interference between the device and lead wires, and electric interference occurs between a device and lead wires.
Further, the conventional fluidic gas meter is provided with an electronic circuit unit made up of a liquid crystal display portion and a circuit portion. In the electronic circuit unit, as shown in FIG. 4, a liquid crystal display portion 201 and a circuit portion 208 which is provided with IC's 202 and 203, resistors 204 to 206 and a capacitor 207, are formed on a circuit board 209 as one body. Alternatively, as shown in FIG. 5, a board 210 mounted with the liquid crystal display portion 201 is electrically connected to another board 211 mounted with the circuit portion 208, by lead wires 212 or a flat cable. In a case where the electronic circuit unit of FIG. 4 is mounted on an electronic gas meter, there arises a problem that the orientation of the liquid display portion is restricted. On the other hand, in a case where the electronic circuit unit of FIG. 5 is used, there arises a problem that the number of steps for connecting the boards 210 and 211 electrically is increased.
Further, in a case where a cord is connected with an electric meter such as an electronic gas meter, each of lead wire included in the cord is connected electrically with a corresponding one of terminals of the electronic meter by a screw or solder, or each lead wire is pressed into electrical contact with a corresponding one of the terminals. As can be seen from the above, in the conventional connecting method, the electrical connection of one lead wire with one terminal is repeated a plurality of times. Thus, there arise problems that the connection of one of the lead wires with a corresponding terminal may be forgotten, and it takes a lot of time to connect the lead wires with the terminals.